USMLE Afibrinogenemia vs von Willebrand Disease?

[Pseudotumor cerebri]

If a 35-year-old woman with heavy menorrhagea since 3-4 years, presents to you after having had a recent paper cut that took longer than usual to heal, and has the following lab findings, what would the differentials be?
Platelets (decreased)
PT/INR - Normal
aPTT - Normal
Platelet aggregation tests - no abnormalities
Everything else - nothing significant

Among the options, I'd narrowed it down to vWD and Afibrinogenemia, but the normal aggregation test threw me off the former, and the age of presentation (and lab findings?) didn't fit with the latter, since it is Autosomal Recessive. Other options given were vit K deficiency and Hemophilia A. What are the possible differential diagnoses?

---

Members don't see this ad.

 

[readerreaderreader]

Honestly there's really not much to go on here. I don't really associate vWD with decreased platelets but I guess that's possible. Did they give you bleeding time?

 

[Pepe18]

.

 

[nintendofriendo]

So you've got increased bleeding time with thrombocytopenia but secondary hemostasis tests are normal...so the answer should be a primary hemostasis disorder, and rules out vit K deficiency as well as hemophilia A.

Like Pepe18 stated above, afibrinogenemia means you would expect decreased platelet aggregation since fibrinogen is supposed to cross-link platelets.

But vWF would also be wrong because vWF is not only involved in platelet adhesion via Gp1b, but it also stabilizes factor 8, so you would expect to see an increased PTT with vWF disease.

So in conclusion, I don't like any of these 4 answers.

 

[Pepe18]

.

 

[Pseudotumor cerebri]

Why would you get normal platelet aggregation with afibrinogenemia? Fibrinogen binds to the gp2b3a receptors on two different platelets, causing aggregation. The fibrinogen is then cleaved to fibrin by thrombin and cross linked by factor 13.

vWF causes platelet adhesion the the endothelium. Without vWF, you still get platelet aggregation, but the aggregate doesn't adhere to the endothelium

Thanks! The point about vWF causing adhesion and not aggregation makes sense. I understand that vWF can still present with normal PT and PTT, and that since it is a qualitative disorder, the platelet count is usually normal? Out of the given options, I suppose vWF makes more sense then?

 

[Pepe18]

.

 

[Interferon Gamma]

Why would you get normal platelet aggregation with afibrinogenemia? Fibrinogen binds to the gp2b3a receptors on two different platelets, causing aggregation. The fibrinogen is then cleaved to fibrin by thrombin and cross linked by factor 13.

vWF causes platelet adhesion the the endothelium. Without vWF, you still get platelet aggregation, but the aggregate doesn't adhere to the endothelium

I agree with the principle but the problem is that for aggregation to occur the initiating event is platelet adhesion to the endothelium causing a conformational change in the platelet and degranulation releasing ADP and TXA2. ADP then acts on P2y12 which upregulates gp2b3a and then fibrinogen binds to it and causes aggregation... I still feel like they didnt write that question right because the platelet aggregation study is the basis of the Ristocetin test right? idk maybe im just salty cuz i didnt chose vWD even though out of all of the options it was the only one that made more sense... I just thought about it long enough to convince myself it was wrong.. haha